Intelligent air moving apparatus

ABSTRACT

An intelligent air moving apparatus for cooling an electronics enclosure includes a motor for driving a fan at a variable rotational speed and a microcontroller for controlling the rotational speed of the motor. The microcontroller includes a speed sensor for sensing the rotational speed such that when the sensed rotational speed deviates below a target speed, the microcontroller detects a locked rotor condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. Provisional Application No. 60/943,679, filed Jun. 13, 2007, entitled “Intelligent High Performance Air Mover.”

BACKGROUND

Fans powered by electric motors are commonly used to cool computer servers and other electronic equipment within an electronics enclosure. Existing electronics enclosure cooling fans have limited intelligence and provide little or no communication to an infrastructure controller capable of monitoring the electronics systems the fans are designed to cool. Therefore, existing fans lack the ability to be optimized for thermal performance, noise, power consumption, reliability, maintenance and warranty costs, and other relevant parameters.

In typical computing systems, including computer servers, multiple fans are required to maintain sufficient airflow to cool the electronics equipment within the enclosure. Further, the multiple fans must be able to operate effectively and harmoniously in conjunction with each other. Therefore, limited intelligence fans require substantial amounts of computational overhead to ensure the fans are operating to provide adequate cooling, and to detect fan failures before the electronics equipment overheats.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate embodiments of an intelligent air moving apparatus as described herein.

In the drawings:

FIG. 1 shows a schematic view of a fan module interconnected to an infrastructure controller.

FIG. 2 shows an electronics enclosure having a plurality of fan modules mounted thereto for providing cooling.

DETAILED DESCRIPTION

There is shown in FIG. 1 an air moving apparatus 100 comprising a fan module 10 interconnected to an infrastructure controller 50. The infrastructure controller 50 is further interconnected to an electronics enclosure 60 to monitor various operational parameters including temperature of the electronics enclosure 60. The fan module 10 comprises a fan 12, a microcontroller 20, and an interface 40. The fan 12 has a motor 14 adapted to drive a fan blade 16 at a variable rotational speed, as commanded by the microcontroller 20, to accommodate the cooling needs of the electronics enclosure 60. The microcontroller 20 controls the speed of the motor 16 and includes a speed sensor 30 to sense the motor rotational speed and to provide a feedback signal of the actual motor speed. The microcontroller can additionally include other sensors, such as a voltage sensor 34, and a current sensor 36. In an embodiment, the microcontroller 20 receives instructions from the infrastructure controller 50 and sends fan status information to the infrastructure controller 50 via the interface 40.

The microcontroller 20 can be a microprocessor. Alternatively, the microcontroller functions can be performed by solid state components or other circuitry. An exemplary microcontroller is commonly known as a Programmable Interface Controller or Programmable Intelligent Computer (“PIC”), an inexpensive chip-based programmable microcontroller. The term “PIC” is used interchangeably with the term “microcontroller” in this application. The microcontroller 20 includes a memory 28 for storing data.

The microcontroller 20 includes features to allow the fan module 10 to assess its own status. The microcontroller 20 further is adapted to communicate information regarding operation of the fan module 10 to the infrastructure controller 50 to facilitate efficient and quiet cooling provided by the fan 12 to the electronics equipment 60. The microcontroller 20 can reduce power consumption and noise generation by the fan module 10, and can increase reliability of the fan 12, optimizing the fan 12 to operate at a level adequate to ensure adequate cooling of the electronics equipment 60 rather than having to operate at a margin of safety above such a level.

Precise Speed Control.

In order to optimize fan module performance, the microcontroller 20 includes a feedback control loop and a speed control algorithm for precisely regulating the rotational speed of the motor 14. In one embodiment, a DC motor is used and motor speed is controlled by pulse-width modulation (PWM). The speed is controlled to a target speed that can be a preprogrammed speed, a speed setpoint received from the infrastructure controller 50, or a default speed at which the fan motor 14 operates in the event of a communication failure between the infrastructure controller 50 and the fan module 10. The default speed can be the most recent target speed received from the infrastructure controller 50 or a preset default speed stored in the memory 28 of the microcontroller 20. The control loop detects the actual rotational speed of the motor 14 as measured or sensed by the speed sensor 30 and the algorithm compares the actual speed to the target speed. The motor rotational speed can be measured periodically over various time spans depending on the accuracy of control required. When the measured speed of the motor 14 deviates from the target speed by at least a preset tolerance, the algorithm adjusts the control signal to the motor 14 to cause the actual motor speed to approach the target speed. Accurate speed control is used to improve power usage and reliability by causing a fan motor 14 to operate only as fast as necessary to achieve the required cooling.

Speed control can also be accomplished by using a thermal sensor (not shown) measuring fan inlet air temperature changes that may be caused by changes to the ambient conditions of the room or loading of the electronic equipment in the enclosure. A target speed can be set based on the fan inlet temperature detected by the thermal sensor. In one example, if the ambient temperature becomes too high (e.g., the room air conditioning fails), the fan can accelerate to a higher speed as required. In another example, if an electrical short causes a visual thermal event (i.e., a fire), the fan can shut down and allow the event to extinguish itself (since most materials in the electronics enclosure are rated to stop burning) rather than aggravating the fire by providing additional air.

In one embodiment, an external crystal oscillator is used to ensure an accurate time base for motor speed measurements. The speed control algorithm can contain optimizations to handle large changes in motor speed settings by attempting to estimate the correct PWM setting for a given motor speed, thereby achieving the target speed faster by making fewer incremental steps. Optimization of the speed control algorithm is particularly useful in the event that the motor speed or target speed changes by a large amount in a short period of time.

Avoidance of Natural and Beat Frequencies.

Providing precise speed control of the motor 14 enables the fan module 10 to avoid natural vibration frequencies. All devices with rotating components, including the fan 12 and fan module 10, have natural vibration frequencies at certain speeds, and often these speeds fall within the range of normal operation. If the device is operated at such speeds, the natural vibration frequencies can cause not only vibrations but also acoustic noise. These natural vibration frequencies can be readily determined, either by theoretical or empirical methods, and correlated with motor speeds, based at least in part on the characteristics of the motor 14, the fan blade 16, and the fan module 10. In an embodiment, speed avoidance data is stored in tables in the memory 28 of the microcontroller 20. The data tables (generally expressed in RPM) establish speed avoidance zones within a predetermined band around each of the natural vibration frequencies. The speed avoidance zone data can be stored in the microcontroller 20 or can be communicated to the microcontroller 20 from the infrastructure controller 50. The microcontroller 20 does not permit the fan 12 to operate within any of the speed avoidance zones. Instead, when cooling requirements call for a speed within a speed avoidance zone, the microcontroller 20 sends the fan motor 14 a speed setpoint that is slightly above or below the prohibited zone, in order to maintain sufficient cooling flow while minimizing power used by the motor 14. The speed setpoint can be outside the avoidance zone by a percentage of the target speed or by a fixed number of RPM, depending on the characteristics of the fan. In one embodiment, the microcontroller 20 controls the fan motor 14 to operate at a speed approximately 100 RPM above or below the speed avoidance zone.

A system 100 may comprise two or more fan modules 10 operating in conjunction to cool an electronics enclosure 60, as shown in FIG. 2. Whenever two similarly sized fans 12 operate nearby each other at similar speeds, there is a potential for beat frequencies to occur. As an extension of the speed avoidance tables, additional speed avoidance zones can be created to avoid such beat frequencies. As with the individual speed avoidance zones, when a target speed is provided to a microcontroller 20 to operate a fan 12 in one of the beat frequency speed avoidance zones, the microcontroller 20 automatically adjusts the rotational speed of the fan 12 to be slightly above the prohibited range in order to prevent unwanted tone resonance and beat frequencies while still achieving at least the minimum speed required to provide proper cooling.

Locked Rotor Protection.

In one embodiment, the fan motor 14 is a conventional DC motor having a stator and a rotor, wherein the fan blade 16 spins along with the rotor while the stator remains stationary with respect to the remainder of the fan 12. If the rotor locks up, the fan blade 16 will not spin and the fan 12 will not be able to deliver cooling. Additionally, a locked rotor can damage the fan 12. There are at least four possible types of locked rotor events that prevent the fan 12 from rotating when it is instructed to rotate by the microcontroller 20: lock-up at startup, lock-up while running at constant speed, lock-up during speed changes, and partial lock-up that creates a drag but does not completely stop the fan blade from spinning. Typically, these events occur when the fan blade 16 is blocked from running due to loose cables or other objects obstructing the fan 12 in one way or another, or due to debris or wear in the bearings of the motor 14.

Some fans in the industry use Hall effect sensors (which sense proper commutation of the motor) to detect situations when a fan is commanded to run but the fan blade or impeller is not spinning as it should. However, in an embodiment in which the fan module 10 is packaged into a very small volume, there is insufficient space for Hall effect sensors. In other embodiments, it may be cost-prohibitive to use Hall effect sensors. Therefore, in order to detect a locked rotor event, the microcontroller 20 employs a speed sensor 30 capable of detecting back electromotive force voltage (back EMF) and correlating the back EMF with fan speed. When the back EMF sensor 30 detects a locked rotor event based on back EMF, a failure alert is generated by the microcontroller 20 and a motor restart sequence is initiated. In an embodiment, the microcontroller 20 is a PIC and this functionality is accomplished by code on the PIC, combined with hardware circuitry. In another embodiment, the microcontroller 20 uses hardware circuitry alone.

Back EMF voltages are tabulated or stored in the memory 28 of the microcontroller 20 for known operating conditions when the fan 12 is operating normally, so they can be compared with voltages measured at various actual operating conditions to detect whether the actual operating conditions have deviated by at least a threshold amount outside normal ranges. The threshold amount can be specified as a percentage of the target speed or as a fixed number of RPM. If such a deviation is detected by the speed sensor 30, a comparator in the microcontroller 20 triggers a restart of the motor 14. Alternatively, the microcontroller 20 can sample the back EMF voltages detected by the speed sensor 30 and code can be used to determine whether the voltage value is normal or abnormal. If abnormal, the microcontroller 20 can instruct the motor 14 to shut down and restart.

In one embodiment, the time to detect a locked rotor condition is dependent upon the target speed of the fan 12, ranging from about 1 second at a high target speed to about 6 seconds at a low target speed. During a shut down and restart, the fan 12 is turned off for about 7 seconds and takes an additional 3-4 seconds to restart. To prevent overheating of the motor 14, the number of restart cycles can be limited, and an alert created when the limit is reached to indicate that the fan 12 needs inspection and/or replacement.

Speed Brake.

Rotating devices such as cooling fans can be dangerous to maintenance or repair personnel. In particular, high performance cooling fans such as the fan 12 can operate at speeds of 18,000 RPM or higher. Therefore, the fan 12 is provided with an electronic speed brake to stop the fan blade 16 from rotating within about one second after when power is removed from the motor 14 or the module 10 is removed, thereby significantly reducing the chance that a service person, tool, or other object will contact rotating fan blades during servicing and/or removal of the fan 12 and/or the fan module 10. The electronic speed brake functions as follows. After power is removed from the motor 14, the voltage sensor 34 senses or detects a corresponding voltage drop indicative of the removal of power. When a predetermined threshold drop in voltage is reached, the microcontroller 20 simultaneously energizes all motor phases, causing the sequenced commutation to stop substantially immediately and thus substantially immediately stopping the fan blades from rotating.

Autonomous Operation.

In one embodiment, the fan module 10 operates autonomously and has intelligence keep the fan 12 running to cool the system even when the microcontroller 20 does not receive a target speed signal from the infrastructure controller 50. Once the fan 12 has been instructed to operate at a rotational speed or RPM setpoint, the fan module 10, through the microcontroller 20 or PIC, is capable of controlling and monitoring its own performance. Therefore, the fan module 10 will maintain the speed of the fan 12 at a target speed. The target speed can be provided by the infrastructure controller 50 or can be stored in the memory 28 of the microcontroller 20.

If the fan 12 is unable to reach or maintain the target speed, the microcontroller 20 communicates an alert signal to the infrastructure controller 50. By having this intelligence built into the fan module 10 as opposed to being centralized in the infrastructure controller 50, the fan 12 can operate to cool the electronics enclosure 60 if the infrastructure controller 50 is not operating or if the fan module 10 loses communication with the infrastructure controller 50. Also, because some electronics enclosures 60 have ten or more cooling fan modules 10, intelligence built into the fan module 10 reduces the computational loading on the infrastructure controller 50.

Sequenced and Gradual Startup.

In a system 100 including multiple fan modules 10, starting two or more fans 12 simultaneously at a desired setpoint speed could result in undesirable power surges. To avoid such power surges, the microcontroller 20 can implement various strategies. In one embodiment, the fans 12 can be started up sequentially. In another embodiment, the fans 12 can be started up at a relatively low speed and then gradually ramped up to the setpoint speed. In yet another embodiment, the fans 12 can be started up sequentially at a relatively low speed and then each fan gradually ramped up to the setpoint speed.

Fan Failure Indicator.

The fan module 10 can include at least one colored light emitting diode (LED) to indicate status conditions of the fan 12. In an embodiment, a green LED 22 and an amber LED 24 are connected to the microcontroller 20. When the fan module 10 is off, i.e., no power is being delivered to the fan 12 and the microcontroller 20 has not been instructed to operate the fan 12, neither LED 22, 24 is illuminated. When power is on and the fan 12 is operating normally, i.e., within a preset range of a target speed, the green LED 22 is illuminated. The present range can be bounded by a percentage of the target speed or by a number of RPM above and/or below the target speed, and can be provided by the infrastructure controller 50 or stored in the memory 28 of the microcontroller 20. When the fan 12 fails to operate, the amber LED 24 is illuminated. Circuitry is included to keep the LED 24 illuminated amber in the event of loss of programming to the microcontroller 20 or corrupted microcontroller memory 28 to help distinguish and diagnose this failure scenario. When an error condition is present that does not prevent the fan 12 from operating, the amber LED 24 blinks. Error conditions can include, but are not limited to, the fan module 10 being installed in an incorrect location, a loss of communication from the infrastructure controller 50 to the fan module 10 (i.e., to the microcontroller 20), and receipt of an override signal. Blinking the amber LED 24 to indicate such conditions helps to diagnose problems prior to an indication from the infrastructure controller 50 of a more serious condition, such as insufficient cooling being provided to the electronics enclosure 60.

Because the microcontroller 20 has the ability to measure both speed of the motor 14 and power drawn by the motor 14, a pre-failure alert can be provided when the microcontroller 20 detects a deviation from the expected relationship between fan speed and power. Such a deviation could be due to bearing wear, debris build-up at the fan inlet, or other conditions requiring attention. Similarly, one or more temperature sensors can be used on the motor 14 to detect deviations from expected normal operating temperatures that can be indicative of impending motor failure.

Interactive Communication.

In one embodiment, the interface 40 is a bi-directional interface through which the fan module 10 can exchange communications with the infrastructure controller 50 via a primary communication link 70. Through the interface 40, the microcontroller 20 communicates operational and other information to enable optimization of fan performance or diagnosis of problems within the fan module 10 in the event of an error condition or failure. The infrastructure controller 50 can instruct the microcontroller 20 to operate the fan 12 at a target rotational speed. Further, the infrastructure controller 50 can read status parameters of the fan 12, as collected by the microcontroller 20 through its various sensors, such as the motor speed and the voltage and current being supplied to the motor 14. The infrastructure controller 50 can also read static and dynamic data stored in the memory 28 of the microcontroller 20. Static data can include identifying information such as spare part numbers, serial numbers, and date of manufacture, as well as operational information such as power-on speed and override PWM setting. Dynamic data can include information such as total hours of motor operation, total revolutions of motor operation, and logged failures or error events (e.g., locked rotor restarts). The infrastructure controller 50 can update the stored data to affect operation of the fan 12, for example to update the speed zone avoidance data and overall speed range settings.

Power Circuit and Overcurrent Protector.

The microcontroller 20 includes a power sensing circuit 38 to measure the power being consumed by the fan 12, thereby enabling the infrastructure controller 50 to monitor and effectively allocate power to the various fan modules 10. The power circuit 38 computes power based on measurements from the voltage sensor 34 and the current sensor 36, and reports dynamic power consumption to the infrastructure controller 50, which tracks power allocation. In addition the power circuit 38 can be used to monitor for impending failures due to bearing wear in the fan motor 14, i.e., to provide a pre-failure notification when the motor 14 is drawing more power than it should for a specified rotational speed.

Conventional power circuits use a “one time” fuse that blows if a threshold current is exceeded. When such a fuse blows, any equipment powered through that fuse ceases to function until the fuse is replaced. In the disclosed embodiment, the power sensing circuit 38 monitors power levels. If the power circuit 38 determines that current being drawn by the fan module 10 is too close to a predetermined shutdown threshold, an overcurrent protector 39 shuts off power while preventing damage to itself. The microcontroller 20 is then able to reset and restart the fan 12, avoiding the need for hardware repair resulting from a high current condition.

Redundant Communication Channels.

In one embodiment, the interface 40 in the fan module 10 uses a bus architecture to provide a communication link 70 to the infrastructure controller 50. In particular, an I2C bus may be used. If the communication link 70 is broken, an alternate signal path 75 is provided from the interface 40 to the infrastructure controller 50. Thus, in the event that the infrastructure controller 50 and interface 40 cannot communicate with one another, the infrastructure controller 50 automatically switches over to the alternate signal path and causes the microcontroller 20 to perform a self diagnostic recovery reset, which in most cases will restore the bus communication link 70 from the infrastructure controller 50 to the interface 40.

As shown in the embodiment illustrated in FIG. 2, a system 100 comprising three fan modules 10 is provided. Any number of fan modules 10 can be provided in a system 100. Because each fan module 10 has an independent microcontroller 20, the fans 12 can be individually controlled to allow fine cooling control and to avoid large current surges caused by changing power states on all fans 12 simultaneously. An infrastructure controller 50 provides control signals to each fan module 10. The fan modules 10 are supplied with 48 VDC and the speed of each fan motor 14 is controlled by a pulse-width modulated (PWM) 5 VDC signal operating at 20 kHz. The speed sensor 30 in each fan module 10 produces a tachometer signal which is used by the microcontroller 20 to determine rotational speed, and cooling capacity can be inferred from the tachometer signal based on the speed versus airflow characteristics of the fan blade 16. In an embodiment, the tachometer signal is produced as an open collector square wave signal four times per revolution of the fan motor 14. If no control signal is received by a particular fan module 10, that module 10 instructs the fan 12 to spin at a default speed. The default speed can be stored in the memory 28 of the microcontroller 20 or can be the most recent target speed provided by the infrastructure controller 50. Each microcontroller 20 generates a fault signal if any one of a number of “error” conditions occurs, and the fault signal is communicated to the infrastructure controller 50 through an interface 40 in the fan module 10.

When installed, each fan module 10 drives a presence signal low, so that if the fan module 10 loses connection with the infrastructure controller 50, the presence signal will go high and the infrastructure controller will be alerted. Each fan module 10 preferably carries in the memory 28 of the microcontroller 20 a unique identifying information (e.g., model and serial numbers) to facilitate tracking of individual fan modules 10. Each fan module memory 28 also records operating characteristics of the fan 12 and stores pre-failure warranty information. 

1. An intelligent air moving apparatus for cooling an electronics enclosure, the apparatus comprising: a motor for driving a fan at a variable rotational speed; a microcontroller for controlling the rotational speed of the motor, the microcontroller comprising a speed sensor for sensing the rotational speed; wherein when the sensed rotational speed falls below a target speed by at least a threshold amount, the microcontroller detects a locked rotor condition and initiates a sequence to shut down and restart the motor.
 2. The air moving apparatus of claim 1, wherein the speed sensor senses back electromotive force from the motor.
 3. The air moving apparatus of claim 1, the microcontroller further comprising a voltage sensor, the motor having one or more phases, wherein when the voltage sensor senses a drop in voltage indicative of removal of power from the motor, the microcontroller simultaneously energizes all motor phases to stop the motor from rotating.
 4. The air moving apparatus of claim 1, the microcontroller further comprising a memory for storing data including speed avoidance zones, wherein when the target speed is within one of the speed avoidance zones, the microcontroller controls the motor speed to be slightly outside said speed avoidance zone.
 5. The air moving apparatus of claim 1, further comprising an interface for electronically communicating between the microcontroller and an infrastructure controller external to the air moving apparatus, wherein when the interface indicates a loss of communication, the microcontroller maintains the rotational speed at a default speed.
 6. The air moving apparatus of claim 1, the microcontroller further comprising memory for storing static data and an interface for electronically communicating between the microcontroller and an infrastructure controller external to the air moving apparatus, wherein the microcontroller communicates the static data to the infrastructure controller via the interface.
 7. The air moving apparatus of claim 1, the microcontroller further comprising memory for storing dynamic data and an interface for electronically communicating between the microcontroller and an infrastructure controller external to the air moving apparatus, wherein the microcontroller communicates the dynamic data to the infrastructure controller via the interface.
 8. The air moving apparatus of claim 1, further comprising an overcurrent protector for shutting down and restarting the motor upon the detection of a high current condition.
 9. The air moving apparatus of claim 1, further comprising an interface having redundant communication channels for electronically communicating between the microcontroller and an infrastructure controller external to the air moving apparatus, the infrastructure controller being adapted to switch between channels when one of the channels fails.
 10. The air moving apparatus of claim 1, further comprising at least one light emitting diode in electronic communication with the microcontroller to indicate at least one status condition of the apparatus.
 11. The air moving apparatus of claim 1, wherein the microcontroller further provides a failure alert when a locked rotor condition is detected.
 12. The air moving apparatus of claim 1, wherein the microcontroller further provides an alert indicating that inspection of the fan is needed after a predetermined number of shut down and restart sequences.
 13. The air moving apparatus of claim 1, wherein the microcontroller further measures power to the motor, and wherein the microcontroller provides a pre-failure alert when a deviation is detected from an expected relationship between the motor rotational speed and the motor power.
 14. The air moving apparatus of claim 1, further comprising a temperature sensor for measuring motor temperature, wherein the microcontroller provides a pre-failure alert when the motor temperature deviates from an expected normal operating temperature.
 15. The air moving apparatus of claim 1, further comprising a temperature sensor for measuring fan air inlet temperature, wherein the microcontroller controls the motor rotational speed based on the fan inlet temperature.
 16. A system for cooling an electronics enclosure, comprising: a plurality of fan modules, each fan module comprising: a motor for driving a fan at a variable rotational speed; a microcontroller for controlling the rotational speed of the motor; an interface for electronically communicating between the microcontroller and an infrastructure controller external to the fan module, the infrastructure controller providing a target speed to the microcontroller; and a memory for storing data including speed avoidance zones; wherein when the target speed falls within one of the speed avoidance zones, the microcontroller controls the motor speed to be slightly outside said speed avoidance zone.
 17. The system of claim 16, the microcontroller comprising a speed sensor for detecting the rotational speed, wherein when the rotational speed sensed by the speed sensor falls below a target speed by at least a threshold amount, the microcontroller detects a locked rotor condition and initiates a sequence to shut down and restart the motor.
 18. The system of claim 16, the microcontroller comprising a voltage sensor, wherein when the voltage sensor senses a drop in voltage indicative of removal of power from the motor, the microcontroller simultaneously energizes all one or more motor phases to stop the motor from rotating.
 19. The system of claim 16, wherein when the interface indicates a loss of communication with the infrastructure controller, the microcontroller maintains the rotational speed at a default speed.
 20. The system of claim 16, the fan module further comprising a crystal oscillator to ensure an accurate time base for motor speed measurements.
 21. A method of cooling an electronics enclosure comprising: providing at least one fan module comprising a multi-phase motor for driving a fan at a variable rotational speed and a microcontroller for controlling the rotational speed of the motor; sensing the rotational speed; and detecting a locked rotor event when the sensed rotational speed falls below a target speed by at least a threshold amount.
 22. The method of claim 21, further comprising: controlling the rotational speed to be outside one or more speed avoidance zones defined by natural frequencies of the fan module.
 23. The method of claim 21, further comprising: when more than one fan module is provided, starting the fans sequentially instead of simultaneously to avoid power surges.
 24. The method of claim 21, further comprising: providing a communications interface adapted to receive a target speed signal; and maintaining the rotational speed at a default speed when the communications interface detects a loss of the target speed signal. 